The invention relates to a comb filter arrangement including at least one delay circuit and an adder, this adder being twice supplied with a video signal modulated on a carrier, which video signals are applied mutually shifted with time.
For PAL signals such state of the art comb filter arrangements are usually structured such that the input signal of the comb filter arrangement reaches an input of the adder undelayed and reaches a second input delayed for the duration of two picture lines. It is then necessary for the delay period of this second signal to have the given value. However, for manufacturing reasons of the delay circuit this delay circuit often does not have the desired value, that is to say, the duration of two picture lines. For video signals according to the NTSC standard the signals applied to the adder have a mutual delay of the duration of one picture line of the video signal. Here too the drawback appears that this value cannot always be exactly adhered to.
Examples for such a comb filter arrangement are the comb filter arrangements for video recorders for filtering out the color under signal. Such an arrangement is known, for example, from Grundig Technische Informationen 3-84, pages 144-150. The arrangement is used for suppressing adjacent track originating crosstalk color under signals in a PAL color signal read from a video tape. Also the comb filter arrangement known from this publication is designed so that the input signal reaches an input of an adder undelayed and a second input delayed for the duration of two picture lines.
This arrangement too has the drawback mentioned above that the sole delay circuit is to have a given delay value.
In such known comb filter arrangements the delay circuit used has the structure of a glass delay line, a CCD (Charge-Coupled Device) delay line, or a digital delay line.